The research objectives of this study are to determine the efficacy of hepatitis B immune globulin (HBIG) in altering the incidence of hepatitis B virus (HBV) infection in infants born 1) to mothers with acute hepatitis B during the 3rd trimester of pregnancy and immediate 2-month postpartum period, and 2) to asymptomatic HBsAg+ carrier mothers. Infants born to mothers with acute type B hepatitis during the delivery period will receive one injection of HBIG within 2 weeks of delivery. All infants will be followed on a monthly basis and tested for evidence of HBV infection. These results will be compared to the 70% HBsAg positivity which we found in infants born to mothers with acute hepatitis B during the past 6 years (historical controls). Infants born to HBsAg+ carrier mothers will be divided into 2 groups according to the maternal HBeAg test. Those born to HBeAg+ mothers will be randomized in a double blind fashion for HBIG or saline placebo treatment. Infants born to HBeAg negative carrier mothers will be similarly randomized. Each infant will be treated within 2 weeks of delivery, and at 4, 8, and 12 months of age. All infants will be followed monthly for evidence of HBV infection. Also, we will follow the children who have been found to be persistently HBsAg+ during the course of this study. This includes clinical evaluation, tests of liver function, HBsAg titers, HBeAg, anti-HBe, DNA polymerase and anti-HBc measurements on a regular basis. If deemed necessary, further clinical studies will be performed to determine the type and extent of the liver disease which may develop. A long term followup is required to elucidate the natural course of the hepatitis B infection in these infants. We are also studying the incidence of HBsAg infection in 1) family members of HBsAg carrier mothers and 2) family members of the persistently HBsAg positive infants. If HBsAg+, then other studies will be performed to determine the type and severity of liver disease in these individuals. With he availability of the immune adherence test for hepatitis A (HA), we plan to study the incidence of type A hepatitis in pregnant females, and look for the presence of anti-HA in the cord blood and newborn infants. Hepatitis A infection will also be studied in the neonates with serial clinical, biochemical and serologic studies.